The operation of a vacuum processing chamber are well known. In this regard, reaction gases are introduced to the vacuum processing chamber, and then RF energy is delivered into the vacuum processing chamber. This RF energy activates or energizes the reaction gas, thereby forming a resulting plasma in the vacuum processing chamber. This plasma is then used to process a semiconductor workpiece which is placed in same. Heretofore, one of the previous practices was to input RF energy of a single frequency onto the lower electrode of the vacuum processing chamber, for example, 13.56 MHz.
Other developments have been made with respect to plasma processing technology for semiconductor workpieces. For example, dual frequency energy input technology has recently been applied to the activation or energizing of reaction gases in the vacuum processing chamber. This technology has enhanced the processing performance of the plasma with respect to the semiconductor workpieces. In this regard, the dual frequency energy inputted at two different frequencies substantially simultaneously into the vacuum processing chamber. For example, in the present invention, a dual frequency combination of 2 MHz, and 60 MHz may be employed.
When inputting RF energy into a vacuum processing chamber, not all RF energies can be inputted without difficulty. One difficulty which arises is that the vacuum processing chamber has a capacitive impedance which exists between the upper and lower electrodes. As a result, a certain reflection ratio to the RF energy input occurs. Consequently, a portion of the RF energy will typically feed back to the input circuit. This usually causes the input circuit to overheat or even become damaged. Moreover, the vacuum processing chamber is equivalent to a load of capacitive impedance relative to the RF generator. Therefore, its impedance is a complex number. Theoretically speaking, when the capacitive impedance is a conjugate match to the impedance of the input circuit, the reflection ratio is minimized and the RF energy can be inputted satisfactorily. Therefore, proper capacitors and inductors are typically inserted into the input network to subsequently form a conjugate match with the capacitive impedance of the vacuum processing chamber. This kind of input network comprising capacitors and inductors has typically been referred to in the art has a RF matching network.
While RF matching networks have worked with varying degrees of success, many shortcomings are attendant with their use. For example, as the high frequency and low frequency inputs are simultaneously connected to the vacuum processing chamber, the corresponding RF matching network becomes electrically coupled to the vacuum processing chamber. Typically, the inputs of the high frequency and low frequency join at one point or location, and a portion of this energy usually does not go into the vacuum processing chamber, but rather the energy travels to each of the RF generators where it damages same. Therefore, a need exists to isolate the RF matching network of the vacuum processing chamber from the high frequency and low frequency inputs. Heretofore, the degree of isolation reached by such RF matching networks have been equal to the power ratio of energy inputted into the RF matching network of the vacuum processing chamber to the energy inputted into the vacuum processing chamber which is about −20 db, or about 1%.
Based upon the great discrepancy between the frequencies which may be provided by the two RF generators, one way to address this problem is to set up a filter before the connection point of each RF matching network, that is, a high frequency notch or filter at the low frequency side, and a low frequency notch or filter at the high frequency side. Thus, the RF energy inputted into the RF matching network provided by each RF generator is filtered.
This solution, while working with some degree of success, has at least two shortcomings. As a first matter, direct filtering of energy causes a great loss of energy, and further reduces the input efficiency. Secondly, filtering of energy will typically cause the notch or filter to heat up. Moreover, large filters are needed for the filtering of high power energy, thus increasing the volume and weight of the resulting equipment, and the costs associated with the design and manufacturing of the same equipment.